I'm fairly new to C# but have extensive experience in Objective-C and OOP. I'm using Json.NET to automatically parse API responses to objects. It so happens that one of the objects returned has a property named protected. Obviously this is a problem, because protected is a keyword for class member declaration.
"protected": true
Is it possible to add a member with the name protected at all?
Is it possible to add setters and getters that get triggered, if the parser tries to set the protected property? (but assign the value to a private member named _protected)
Should I modify the parser to behave different when he encounters a property named protected?
Thanks for any advice.
1:
For question #1: You can put an # symbol before it any keyword you want to use as a variable name.
E.g.
public string #protected {get; set; }
I recommend against doing this, however. You should be able to remap the "protected" field in your JSON to a different property in your POCO.
2:
private string _protected;
public string #protected
{
get
{
//any additional code you want
return _protected;
}
set
{
//any additional code you want
_protected = value;
}
}
3:
Up to you!
I implemented this solution:
[JsonProperty("protected")] public bool Protected { get; set; }
Like Daniel Mann suggested in his comment:
Related
In C#, can you use a property without a field?
Edit for clarification:
private string _name;
public string Name
{
get { return _name; }
set { _name value; }
}
It seem's like they are always paired, is there a circumstance where we don't use the field at all?
All properties must have a field, assuming they are simple properties to store a value (*). However, the language (as of version 3.0) offers a way to declare the field implicitly. For example:
public int Value { get; set; }
That would declare a property named Value with an implicit field backing it and the getter and setter both public. You can include an accessibility keyword on either the getter or setter to restrict access to the property. For example:
public int Value { get; private set; }
In this case, only the owning type may call the setter, but any class can call the getter.
The next version of C# will have additional features for dealing with these "automatic properties", allowing you to provide a concise initialization syntax for them. For now, you have to initialize them in a constructor.
EDIT: based on your edited question, it seems worthwhile to address this specific question: "is there a circumstance where we don't use the field at all?"
The answer to that is, it's not common for no field to be involved at all. But it is possible, and it's not uncommon for a property to not use a field as storage for the property. For example, imagine a Rectangle object with an Area property:
class Rectangle
{
public double Width { get; private set; }
public double Height { get; private set; }
public double Area { get { return Width * Height; } }
}
Obviously there are fields involved (two of them), but there is not a field specifically dedicated to the Area property.
Another example would be where the property delegates. For example, in a WinForms Form subclass, it's common to expose specific control values via a property:
class MyForm : Form
{
public string EditText
{
get { return textBox1.Text; }
set { textBox1.Text = value; }
}
}
Again, the textBox1 field is being used here. But it actually represents something other than the property itself. The property is using a member of the object that field references.
I hope that clarifies the relationship between fields and properties adequately for you. Please feel free to ask for further clarifications if needed.
(*) Note that the only real rule for properties is that they have at least one of the getter or setter, and those methods can do whatever you want. I assume we are talking about simple value-based properties here.
A property is not required to have a field
public string Version
{
get
{
return "1.3.Awesome";
}
}
If you're asking what I think you are, the answer is yes, you just put get; set; inside the property declaration. C# encapsulates a variable for you.
EDIT: example
//no need for field declaration
public string Name
{
get;
set;
}
This question already has answers here:
Public Fields versus Automatic Properties
(14 answers)
Closed 9 years ago.
Someone told me that you could replace the following code:
private string name;
public string Name
{
get;
set;
}
with the following and suffer no ill effects:
public string Name;
I realize that the property, set like in the first example does pretty much the same as it would if I removed it and set the original attribute to publicbut is it bad programming practice to go with the second way for attributes for which you need just the basic getter and setter?
The second way isn't a property, it's a field. The reason you should always use properties for public-facing values is that converting from a field to a property constitutes a breaking change. Using a property allows you to later change the behavior of the getter or setter without breaking any code that references yours.
Keep in mind, the code
public string Foo { get; set; }
is actually equivalent to
private string foo;
public string Foo
{
get { return foo; }
set { foo = value; }
}
When you use Properties you have better control of what properties have.
private string name;
public string Name
{
get;
set;
}
is wrong it should be either
public string Name
{
get;
set;
}
or
private string name;
public string Name
{
get { return name;}
set { this.name = value;}
}
sometimes when you want variable to be set only inside class u can use
public string Name
{
get;
private set;
}
Properties combine aspects of both fields and methods. To the user of an object, a property appears to be a field, accessing the property requires exactly the same syntax. To the implementer of a class, a property is one or two code blocks, representing a get accessor and/or a set accessor. The code block for the get accessor is executed when the property is read; the code block for the set accessor is executed when the property is assigned a new value. A property without a set accessor is considered read-only. A property without a get accessor is considered write-only. A property with both accessors is read-write.
Source: http://msdn.microsoft.com/en-us/library/w86s7x04(v=vs.80).aspx
I think the shortest way is to use Auto-Implemented Properties and some referenced information about them
In C# 3.0 and later, auto-implemented properties make property-declaration more concise when no additional logic is required in the property accessors. They also enable client code to create objects. When you declare a property as shown in the following example, the compiler creates a private, anonymous backing field that can only be accessed through the property's get and set accessors.
public string Name{ get; set;}
public string Name { get; set; }
msdn :
A property is a member that provides a flexible mechanism to read, write, or compute the value of a private field. Properties can be used as if they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily and still helps promote the safety and flexibility of methods.
A public property isn't the same as a public instance variable.
And this difference can matter.
For instance, if you're using databound asp.net controls like DataTextField from DroDownListBox, it will fail if you set it to a instance variable instead of a public property.
The shortest way of writing a property is using automatic getters and setters.
This is not quite what you've put in your question though, you've replaced a traditional property that has a backing field, with a field.
An automatic getter/setter looks like this:
public string Blah { get; set; }
This feature was introduced in C# 3, I believe. So you have to target this, or above, in order to use these.
I'm trying to do this:
public string LangofUser
{
get
{
return string.IsNullOrEmpty("how to get value?") ? "English" : "how to get value?";
}
set;
}
do I have to do this?
string _LangofUser
public string LangofUser
{
get
{
return string.IsNullOrEmpty(_LangofUser) ? "English" : _LangofUser;
}
set { _LangofUser = value};
}
This mixing of auto-implement and not-auto-implemented properties in C# is not possible. A property must be fully auto-implemented or a normal property.
Note: Even with a fully auto-implemented property there is no way to reference the backing field from C# source in a strongly typed manner. It is possible via reflection but that's depending on implementation details of the compiler.
As others have said, don't try to mix automatic and regular properties. Just write a regular property.
If you want to know what secret names we generate behind the scenes for hidden compiler magic, see
Where to learn about VS debugger 'magic names'
but do not rely on that; it can change at any time at our whim.
If you provide your own implementation of the property, it's not automatic any more. So yes, you need to do create the instance.
Check this question
What's the difference between encapsulating a private member as a property and defining a property without a private member?
If you want to keep the automatic property and still have a default value, why don't you initialize it in your constructor?
public class MyClass
{
public MyClass() { LangOfUser = "English"; }
public string LangOfUser { get; set; }
}
Since C# 6, you can also set a default value for a property as follows:
public class MyClass
{
public string LangOfUser { get; set; } = "English";
}
Today, I was cleaning up some of my code with FXCop and it complained about a Attribute class I had with this violation.
CA1019: Define accessor for attribute argument.
On this page, http://msdn.microsoft.com/en-us/library/ms182136.aspx there is more information, but I still do not get the reason for this as it seems to me more verbose and less relevant.
It gives two codes samples.
using System;
namespace DesignLibrary
{
// Violates rule: DefineAccessorsForAttributeArguments.
[AttributeUsage(AttributeTargets.All)]
public sealed class BadCustomAttribute :Attribute
{
string data;
// Missing the property that corresponds to
// the someStringData parameter.
public BadCustomAttribute(string someStringData)
{
data = someStringData;
}
}
// Satisfies rule: Attributes should have accessors for all arguments.
[AttributeUsage(AttributeTargets.All)]
public sealed class GoodCustomAttribute :Attribute
{
string data;
public GoodCustomAttribute(string someStringData)
{
data = someStringData;
}
//The constructor parameter and property
//name are the same except for case.
public string SomeStringData
{
get
{
return data;
}
}
}
}
I don't understand why the SomeStringData property is required. Isn't the someStringData a parameter? Why does it need to have its own property if it is already stored in another property?
Actually, mine is a little different as it looks like this.
[AttributeUsage(AttributeTargets.Property)]
public sealed class ExampleAttribute : Attribute
{
public ExampleAttribute(string attributeValue)
{
this.Path = attributeValue;
}
public string Name
{
get;
set;
}
// Add to add this to stop the CA1019 moaning but I find it useless and stupid?
public string AttributeValue
{
get
{
return this.Name;
}
}
}
Rather than a private field, I have used a public autoproperty, I had to add the last part to make the warning stop but I don't see the point and it also adds another public field to this class, which is redundant, and seems less clean.
That said, I assume that this warning is raised for a reason so what good reason I am missing here?
Thanks in advance.
FxCop is complaining because your existing property doesn't match the parameter name.
Therefore, it doesn't realize that the parameter actually is exposed.
You should rename the property or parameter to match (except for case), or suppress the warning.
FxCop rule CA1019 is just enforcing the .Net Framework coding guidelines for Attributes.
Use named arguments (read/write properties) for optional parameters. Provide a read/write property with the same name as each named argument, but change the case to differentiate between them.
Documentation Link: http://msdn.microsoft.com/en-us/library/2ab31zeh(v=vs.71).aspx
The reason behind the FxCop warning is that every piece of data you pass into the attribute's constructor should be made publicly available to access when the attribute instance is being retrieved by Reflection.
Let's say you have this:
[BadCustom("My String Data")]
public class DecoratedClass
{
}
How will you get "My String Data" back from that attribute instance when you read it using:
BadCustomAttribute attr = typeof(DecoratedClass)
.GetCustomAttributes(typeof(BadCustomAttribute), false)
.Single() as BadCustomAttribute;
Now you have the instance of your attribute, but no way to read the string passed into the constructor because you didn't at least declare a read-only property for it.
the idea is that you should write just:
[AttributeUsage(AttributeTargets.Property)]
public sealed class ExampleAttribute : Attribute
{
public ExampleAttribute(string attributeValue)
{
this.AttributeValue = attributeValue;
}
public string AttributeValue
{
get;
set;
}
}
This violation will also be thrown when the parameter name matches the property name, but the data types are different.
I've never really questioned this before until now. I've got an input model with a number of fields, I wanted to present the string names of the properties through the input model so that my Grid can use them:
public class SomeGridRow
{
public string Code { get;set; }
public string Description { get;set; }
public const string Code = "Code";
}
Obviously, this gives the error:
The type 'SomeGridRow' already
contains a definition for 'Code'
Why can the CLR not cope with two properties of the same name which are, in my eyes, separate?
string code = gridRow.Code; // Actual member from instantiated class
string codeField = SomeGridRow.Code; // Static/Const
I'm now just using a child class called Fields within my inputs now, so I can use SomeGridRow.Fields.Code. It's a bit messy, but it works.
Because you can also access static (or, non-instance in this case) properties in the same way (inside the same class), and it would be a bit confusing, for example:
public class SomeGridRow
{
public string Code { get;set; }
public const string Code = "Code";
public void MyMethod() {
var thing = Code; //what would this reference?
}
}
Because both this:
public class SomeGridRow
{
public string Code { get;set; }
public void MyMethod() {
var thing = Code; //what would this reference?
}
}
And this:
public class SomeGridRow
{
public const string Code = "Code";
public void MyMethod() {
var thing = Code; //what would this reference?
}
}
are valid ways to access properties, static or not. It doesn't answer the "why can't I?" question, but more of the why it's not allowed...it would be far too ambiguous IMO.
It probably could, but the designers of C# wanted to avoid ambiguities that can come from such use (abuse?) of language features.
Such code would end up being confusing and ambiguous to users (did I want the instance or the static method call?, Which one is right?).
In addition to the points already made about ambiguity, i would say that the naming needs to be relooked in such a case.
If two variables / fields having the exact same name in the same context i.e class but different values to me sounds more like a naming issue.
If they are exactly same, you dont need 2 fields.
If they are slightly different, you should have more accurate names.
In some other languages with a similar syntax, one can access a static member through an instance. So you could access both string.Empty and "abc".Empty.
C# doesn't allow this (though it does sort of from inside the class or a derived class, in that you can omit the class name for a static member and can omit this for an instance member), primarily to avoid confusion (I find it more handy than confusion tbh, but that's just me, I like switch fall-through too so what do I know).
Having introduced a stricter rule to allow for less ambiguity, it would be counterproductive to allow a new looser rule on the back of it that allowed for more. Think how many "why must I use this with property X but not property Y?" questions SO would have if it was allowed (we'd have to force this with property X to be clear we meant the instance member).